Hiroshima by John Hersey published in 1946 and revised in 1985. If you are interested to learn what a nuclear bomb does to people and the city in which they live, read this book. And consider its implications if Donald Trump starts a war in Korea.
Hiroshima largely escaped US fire bombing in WW2 because US war planners wanted an undamaged target so that we could assess how much damage a single nuclear explosion could cause. Then three days later, we bombed Nagasaki with a nuclear bomb of a different design so that we could compare results.
We knew beforehand that the Japanese were willing to surrender and that further bombing was unnecessary. The bombing of Hiroshima and Nagasaki were crimes committed in time of war. Were they war crimes? Yes, I believe they were.